In the daily use of a vehicle, especially in city or other congested traffic, the vehicle will often run in an idling state. Not only is this a waste of fuel for the vehicle operator, it is additionally harmful to the environment, due to the exhaust emissions of the vehicle.
In order to lessen such waste, some vehicles have already been equipped with an automatic start-stop system. In a conventional system, the engine of the vehicle will be automatically stopped when a pre-determined stopping condition occurs, such as idling of the engine for a certain length of time. The engine will then be restarted upon another signal, usually from the driver of the vehicle. These signals may be one such as having the driver touch the gear shift lever. Some systems merely evaluate conditions, such as the engine idle time, to determine when to stop; others monitor specific vehicular conditions, such as the temperature of exhaust gas purifying catalysts, in order to preserve the environment. Such systems are disclosed in U.S. Pat. Nos. 5,566,774 and 6,202,776. However, drive systems using methods such as these have had many problems that have hindered more universal adoption.
For example, the resonation frequency of the engine mounting system may coincide with a rotating frequency of the engine on deceleration. The harmonic resonance of both together can cause the car to shake. Additionally, a vehicle operator may experience a time lag during automatic engine restart. This time lag is due to the time associated with engine cranking and firing. A vehicle may also end up immobilized in traffic. If the automatic start-stop method stops the engine, but fails to successfully restart it, the vehicle may become stranded in the middle of a street, causing a distraction to other drivers and danger to the operator. Outside conditions may also make restart difficult, such as the ambient temperature.